1. The Field of the Invention
The present invention relates to devices and methods for manufacturing medical thermoplastic catheter devices that are adapted for insertion into the body.
2. The Relevant Technology
A catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, access by surgical instruments, delivery of medical devices (e.g., stents), and the like. Medical vascular catheters are particularly designed for insertion into the vasculature and are available for a wide variety of purposes, including diagnosis, interventional therapy, drug delivery, drainage, perfusion, and the like. Medical vascular catheters for each of these purposes can be introduced to numerous target sites within a patient's body by guiding the catheter through an incision made in the patient's skin and a blood vessel and then through the vascular system to the target site. Since it can be difficult to steer many types of catheters, guide wires are often used to help position the catheter.
A medical catheter can be a relatively simple tube that is inserted into a patient's body during a medical procedure or it can be a complicated device that is itself configured to perform a variety of interventional medical procedures. The catheter body may be relatively straight, or may inherently curve, or may be curved by insertion of a curved stiffening wire or guide wire through the catheter lumen. The catheter body and catheter side wall are typically fabricated and dimensioned to minimize the catheter body outer diameter and side wall thickness, and to maximize the catheter lumen diameter while retaining sufficient side wall flexibility and strength characteristics to enable the catheter to be used for the intended medical purpose.
Medical vascular catheters are specifically adapted to be inserted into a patient's vasculature. One type of medical vascular catheter is a so-called “balloon catheter.” A balloon catheter is an elongate tubular member that typically includes an inner tubular member that extends from the proximal end to the distal end, a balloon sealed to the distal end of the inner tubular member, an outer tubular member disposed over the inner tube and sealed to the proximal end of the balloon, and, optionally, a soft, atraumatic tip attached to the distal end of the balloon. The balloon catheter may also include one or more radiopaque markers that allow the progress of the catheter to be tracked in the body with the use of fluoroscopy. The balloon is typically inflated by delivering a pressurized gas or fluid to the balloon through the lumen between the inner and outer tubular members.
One example of a therapeutic procedure performed with a medical vascular catheter is known as percutaneous transluminal coronary angioplasty (“PTCA”). PTCA can be used, for example, to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. In PTCA, a guide wire is typically inserted into the vicinity of a target treatment site in an artery (e.g., a coronary artery). The guide wire can then be used to guide a catheter, such as a balloon catheter, to the treatment site. Inflation of the balloon catheter at the treatment site can be used to compress plaque deposits against the walls of the artery and/or to expand a stent against the walls of the artery, thereby improving or restoring blood flow through the artery.
In order to allow the catheter to traverse the patient's vasculature, facilitate treatment, and prevent additional trauma to the patient, catheters typically need to have a number different sections (e.g., balloon sections, stiffer sections, and more flexible sections) formed from different materials. It should also be noted that in order to allow the catheter to traverse the patient's vasculature, facilitate treatment, and prevent additional trauma to the patient, catheters typically need to be quite small. An inner diameter of about 0.5 mm to 1.5 mm and an outer diameter of about 1 to 3 mm is typical for balloon catheters. Catheters for mitral valve replacement are some of the larger catheters in current use, with an outer diameter in a range from about 6-7 mm.
Such catheters are typically manufactured by “dry fitting” the various sections together, securing a heat-shrink material around the dry fitted sections to temporarily secure the joints, welding the joints together using heat and/or irradiation (e.g., laser irradiation), and finally removing the heat-shrink material from the joint sections. Such methods are complicated and time consuming. Because the material sections used to assemble a catheter are typically quite small and delicate, “dry fitting” the parts together and applying heat-shrink material can be complicated and time consuming. Likewise, using the current state of the art, it is difficult to control the amount of heat yielded by irradiation to weld the various sections together without damaging the tubing parts. As a result, the current state of the art is prone to yield poor uniformity of the welds. The process of removing heat-shrink material is also time-consuming and difficult and, as a result, catheters can be damaged in the process of removing the heat-shrink material, leading to waste.